The invention is directed to detection and intensity measuring of low intensity light beam signals and more particularly to the optical and electrical separation of the low intensity light beam signal from a very much stronger pump light beam signal by using a combination of a simple optical and electrical filtering techniques.
U.S. Pat. No. 1,678,653 by inventor Fritz Schroeter teaches filtering radio signals with a high static content by rectifying and converting the static radio signal into two 90.degree. polarized light wave signals and blending together the two signals. The static component is cancelled in this manner and the radio wave signal remaining represents the transmitted radio frequency signal. This resulting radio wave signal is then recorded on a light sensitive medium from which it is converted to a readable message. This patent teaches converting radio signals (electrical) to visual (light wave) signals. There is no attempt to measure the intensity of the resulting light signal.
A large body of literature exists on various methods for frequency conversion one of which envisions the concepts of the present invention. The major problem that has not been overcome by the prior art is how to separate a weak signal light beam combined with a strong pump light beam from the strong pump beam. The present invention overcomes this major problem.